Vertical light emitting diode and method of manufacturing the same

ABSTRACT

Provided is a vertical LED including an n-electrode; an n-type GaN layer formed under the n-electrode, the n-type GaN layer having a surface coming in contact with the n-electrode, the surface having a Ga + N layer containing a larger amount of Ga than that of N; an active layer formed under the n-type GaN layer; a p-type GaN layer formed under the active layer; a p-electrode formed under the p-type GaN layer; and a structure support layer formed under the p-electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2006-0102967 filed with the Korean Intellectual Property Office onOct. 23, 2006, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vertical light emitting diode (LED)and a method of manufacturing the same, which can reduce contactresistance of an negative electrode formed on the surface of an n-typeGaN layer and can enhance thermal stability.

2. Description of the Related Art

Generally, a nitride-based semiconductor LED is grown on a sapphiresubstrate, but the sapphire substrate is a rigid nonconductor and haspoor thermal conductivity. Therefore, there is a limitation in reducingthe manufacturing costs by reducing the size of a nitride-basedsemiconductor LED, or improving the optical power and chipcharacteristic. Particularly, because the application of a high currentis essential for achieving high power LED, it is important to solve aheat-sink problem of the LED. To solve this problem, there has beenproposed a vertical LED in which a sapphire substrate is removed usingLaser Lift-Off (LLO).

Hereinafter, a conventional vertical LED will be described in detailwith reference to FIG. 1. FIG. 1 is a cross-sectional view of aconventional vertical LED.

As shown in FIG. 1, the conventional vertical LED has a structuresupport layer 150 formed in the lowermost portion and a positive (p-)electrode 140 formed on the structure support layer 150. Preferably, thep-electrode 140 is formed of a conductive reflecting member serving asan electrode and a reflecting layer.

On the p-electrode 140, a p-type GaN layer 130, an active layer 120, andan n-type GaN layer 110 are sequentially formed, thereby forming a lightemission structure.

An upper portion of the light emission structure, that is, the surfaceof the n-type GaN layer 110 has surface irregularities (not shown) forenhancing light emission efficiency. On the n-type GaN layer 110, anegative (n-) electrode 160 is formed.

In the conventional vertical LED, however, the surface of the n-type GaNlayer 110 coming in contact with the n-electrode 160 is an N-face orN-polar surface which comes in contact with a sapphire substrate (notshown) on which the n-type GaN layer is formed.

When the n-electrode 160 is positioned on the n-type GaN layer 110having an N-face or N-polar surface, the contact resistance of then-electrode increases, and thus an operational voltage of the LEDincreases. As a result, a heating value increases.

As such, when a heating value increases so that the thermal stability ofthe vertical LED decreases, the contact resistance of the LED alsocontinuously increases, thereby degrading characteristics andreliability of the vertical LED.

SUMMARY OF THE INVENTION

An advantage of the present invention is that it provides a vertical LEDin which the surface of an n-type GaN layer coming in contact with ann-electrode is formed of a Ga⁺N layer containing a larger amount of Gathan that of N, that is, the surface electron concentration of then-type GaN layer is increased. In the vertical LED, the contactresistance of the n-type GaN layer coming in contact with then-electrode and having an N-face or N-polar surface can be reduced, andthermal stability can be enhanced.

Another advantage of the invention is that is provides a method ofmanufacturing the vertical LED.

Additional aspect and advantages of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the general inventive concept.

According to an aspect of the invention, a vertical LED comprises ann-electrode; an n-type GaN layer formed under the n-electrode, then-type GaN layer having a surface coming in contact with then-electrode, the surface having a Ga⁺N layer containing a larger amountof Ga than that of N; an active layer formed under the n-type GaN layer;a p-type GaN layer formed under the active layer; a p-electrode formedunder the p-type GaN layer; and a structure support layer formed underthe p-electrode.

The n-electrode may be formed of a single layer composed of one or moremetals selected from the group consisting of Ti, Ta, and Zr.Alternately, the n-electrode may be formed of a multilayer in which morethan two layers including a layer composed of one or more metalsselected from the group consisting of Ti, Ta, and Zr are laminated.

The Ga⁺N layer of the n-type GaN layer may be formed by laser-treatingor heat-treating the surface of the n-type GaN layer coming in contactwith the n-electrode.

The p-electrode may be formed of a conductive reflecting member.Further, the Ga⁺N layer coming in contact with the n-electrode may havesurface irregularities formed thereon.

According to another aspect of the invention, a method of manufacturinga vertical LED comprises forming a light emission structure in which ann-type GaN layer, an active layer, and a p-type GaN layer aresequentially laminated on a substrate; forming a p-electrode on thelight emission structure; forming a structure support layer on thep-electrode; removing the substrate to expose the n-type GaN layer;laser-treating the surface of the exposed n-type GaN layer to form a Galayer and a Ga⁺N layer which are sequentially laminated from thelaser-treated surface; and forming an n-electrode on the laser-treatedsurface of the n-type GaN layer.

Preferably, the laser-treatment is performed using laser with awavelength having energy larger than an energy band gap of GaN.

Preferably, the method further comprises forming surface irregularitieson the laser-treated surface of the n-type GaN layer, before the formingof the n-electrode.

According to a further aspect of the invention, a method ofmanufacturing a vertical LED comprises forming a light emissionstructure in which an n-type GaN layer, an active layer, and a p-typeGaN layer are sequentially laminated on a substrate; forming ap-electrode on the light emission structure; forming a structure supportlayer on the p-electrode; removing the substrate to expose the n-typeGaN layer; heat-treating the surface of the exposed n-type GaN layer toform a Ga layer and a Ga⁺N layer which are sequentially laminated fromthe heat-treated surface; and forming an n-electrode on the heat-treatedsurface of the n-type GaN layer.

Preferably, the heat-treatment is performed at a temperature of morethan 500° C.

Preferably, the method further comprises forming surface irregularitieson the laser-treated surface of the n-type GaN layer, before the formingof the n-electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1 is a cross-sectional view of a conventional vertical LED;

FIG. 2 is a cross-sectional view of a vertical LED according to anembodiment of the invention; and

FIGS. 3A to 3F are sectional views sequentially showing a process forexplaining a method of manufacturing a vertical LED according to anembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentgeneral inventive concept, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to likeelements throughout. The embodiments are described below in order toexplain the present general inventive concept by referring to thefigures. In the drawings, the thicknesses of layers and regions areexaggerated for clarity.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

Structure of Vertical LED

Referring to FIG. 2, the structure of a vertical LED according to anembodiment of the invention will be described in detail.

FIG. 2 is a cross-sectional view of a vertical LED according to anembodiment of the invention.

As shown in FIG. 2, the vertical LED has an n-electrode 160 formed inthe uppermost portion thereof. Preferably, the n-electrode 160 is formedof a single layer composed of one or more metals selected from the groupconsisting of Ti, Ta, and Zr forming a nitride or a multilayer in whichmore than two layers including a layer composed of one or more metalsselected from the group consisting of Ti, Ta, and Zr are laminated, inorder to increase the electron concentration of a Ga⁺N layer which willbe described below. As for the multilayer, Ti/Al/Ti/Au or Ti/Al,Ta/Al/Ti/Au, Ti/Au, TiTa/Au and the like are exemplified.

Under the n-electrode 160, an n-type GaN layer 110 is formed.

In a general vertical LED, the n-type GaN layer 110 is formed on asapphire substrate by an epitaxial growth method, and the sapphiresubstrate is then removed. Therefore, the surface of the n-type GaNlayer 110, which comes in contact with the n-electrode 160, is an N-faceor N-polar surface.

However, when the n-electrode 160 is positioned on the n-type GaN layer110 having an N-face or N-polar surface, the contact resistance of then-electrode 160 increases as in the related art. Therefore, anoperational voltage of an LED is increased so that a heating valueincreases.

To solve such a problem, the surface of the n-type GaN layer 110 comingin contact with the n-electrode 160 is formed of a Ga⁺N layer 110 ccontaining a larger amount of Ga than that of N. That is, the Ga⁺N layer110 c serves to increase the electron concentration of the surface ofthe n-type GaN layer 110 coming in contact with the n-electrode 160.

In other words, the n-type GaN layer 110 has such a structure that theGa⁺N 110 c containing a larger amount of Ga than that of N and a GaNlayer 110 a are sequentially laminated under the n-electrode 160. TheGa⁺N layer 110 c is formed by the following process. The surface of theGaN layer 110 a adjacent to the n-electrode 160 is laser- orheat-treated so that GaN is separated into Ga and N elements. Then, theGa⁺N layer 100 c is formed.

As described above, when the surface of the n-type GaN layer 110 comingin contact with the n-electrode 160 is formed of the Ga⁺N 110 c havinghigh electron concentration, a Schottky barrier height is reduced,thereby reducing contact resistance. As a result, it is possible toenhance thermal stability of the vertical LED.

Meanwhile, although not shown, the surface of the n-type GaN layer 110coming in contact with the n-electrode 160, that is, the surface of theGa⁺N layer 110 c is preferably formed with surface irregularities forincreasing light extraction efficiency.

Under the n-type GaN layer 110, an active layer 120 and a p-type GaNlayer 130 are sequentially laminated, thereby forming an LED lightemission structure.

In the LED light emission structure, the p-type GaN layer 130 may be aGaN layer or GaN/AlGaN layer doped with p-type impurities, and theactive layer 120 may be formed with a multi-quantum well structurecomposed of an InGaN/GaN layer.

Under the p-type GaN layer 130 of the LED light emission structure, ap-electrode 140 is formed. Preferably, the p-electrode 40 serves as anelectrode and a reflecting layer. Accordingly, the p-electrode 40 isformed of a conductive reflecting member.

Although not shown, a p-electrode and a reflecting layer may besequentially laminated under the p-type GaN layer 130.

Under the p-electrode 140, a structure support layer 150 is bondedthrough a conductive bonding layer (not shown). The structure supportlayer 150 serves as a support layer of a finalized LED and an electrodeand is formed of a Si substrate, a GaAs substrate, a Ge substrate, or ametal layer. The metal layer can be formed by electroplating,electroless plating, thermal evaporating, e-beam evaporating,sputtering, Chemical Vapor Deposition (CVD) or the like.

Method of Manufacturing Vertical LED

Referring to FIGS. 3A to 3F and 2, a method of manufacturing a verticalLED according to an embodiment of the invention will be described indetail.

FIGS. 3A to 3F are sectional views sequentially showing a process forexplaining a method of manufacturing a vertical LED according to anembodiment of the invention.

First, as shown in FIG. 3A, an LED light emission structure, in which ann-type GaN layer 110, a GaN/InGaN active layer 120 with a multi-quantumwell structure, and a p-type GaN layer 130 are sequentially laminated,is formed on a substrate 100.

Preferably, the substrate 100 having the LED light emission structureformed thereon is formed of a transparent material including sapphire.In addition to sapphire, the substrate 100 may be formed of zinc oxide(ZnO), gallium nitride (GaN), silicon carbide (SiC) or aluminum nitride(AlN).

The n-type GaN layer 110, the active layer 120, and the p-type GaN layer130 may be formed by a known nitride deposition process such asMetal-Organic Chemical Vapor Deposition (MOCVD) or the like.

The active layer 120 may be formed of one quantum-well layer or may beformed with a double-hetero structure.

Next, as shown in FIG. 3B, a p-electrode 140 and a structure supportlayer 150 are sequentially formed on the LED light emission structure,that is, on the p-type GaN layer 130.

Preferably, the p-electrode 140 is formed of a conductive reflectingmember such that light generated from the active layer 120 is preventedfrom being absorbed into the structure support layer 150.

The structure support layer 150 serves as a support layer and anelectrode of a finalized LED and is formed of a Si substrate, a GaAssubstrate, a Ge substrate, or a metal layer. The metal layer can beformed by electroplating, electroless plating, thermal evaporating,e-beam evaporating, sputtering, CVD or the like.

Subsequently, as shown in FIG. 3C, the substrate 100 is separated fromthe LED light emission structure, that is, the n-type GaN layer 110 suchthat the n-type GaN layer 110 is exposed.

At this time, the substrate 100 is removed using a Laser Lift-Off (LLO)method, a Chemical Lift-Off (CLO) method, a Chemical MechanicalPolishing (CMP) method or the like.

Then, as shown in FIG. 3D, the surface of the exposed n-type GaN layer110 is laser- or heat-treated by a predetermined thickness in adirection of the arrow. At this time, only the surface of the n-type GaNlayer 110 is modified by the predetermined thickness. Preferably, themodified surface has a thickness of less than several hundreds nm.

Preferably, the laser treatment is performed using laser with awavelength having energy larger than an energy band gap (3.3 eV) of GaN.More specifically, 248 nm KrF laser (5 eV) or 193 nm ArF laser (6.4 eV)is used.

Further, the heat treatment is performed at a temperature of more than500° C. such that GaN forming the N-type GaN layer 110 can be separatedinto Ga and N elements.

Then, as shown in FIG. 3E, the n-type GaN layer 110 has such a structurethat a Ga layer 110 b, a Ga⁺N layer 110 c, and a GaN layer 110 a aresequentially laminated from the surface of the n-type GaN layer 110coming in contact with the n-electrode 160. At this time, while theseparated N elements pass through the Ga layer 110 b so as to beevaporated, the Ga⁺N layer 110 c has an N-vacancy structure. That is,the Ga⁺N layer 110 c is a portion of the n-type GaN layer 110, whereelectron concentration has increased.

Next, as shown in FIG. 3F, the Ga layer 110 b is removed using achemical solution such as HCl or the like. In this case, the removing ofthe Ga layer 110 b is not necessarily performed. The reason why theremoving is performed is for improving adhesive strength with ann-electrode which will be described below.

After that, an n-electrode 160 is formed on the Ga⁺N layer 110 c exposedby removing the GaN layer 110 b (refer to FIG. 2).

Preferably, the n-electrode 160 is formed of a single layer composed ofone or more metals selected from the group consisting of Ti, Ta, and Zrforming a nitride or a multilayer in which more than two layersincluding a layer composed of one or more metals selected from the groupconsisting of Ti, Ta, and Zr are laminated, in order to increase theelectron concentration of the Ga⁺N layer positioned under then-electrode 110 c. As for the multilayer, Ti/Al/Ti/Au or Ti/Al,Ta/Al/Ti/Au, Ti/Au, TiTa/Au and the like are exemplified.

According to the vertical LED of the invention, the surface of then-type GaN layer coming in contact with the n-electrode is formed of aGa⁺N layer, containing a larger amount of Ga than that of N, such thatthe surface electron concentration of the n-type GaN layer is increased.Therefore, when the n-electrode comes in contact with the n-type GaNlayer having an N-face or N-polar surface, the Schottky barrier heightis reduced so that contact resistance can be reduced.

Further, when the contact resistance of the n-electrode is reduced, anoperational voltage of the LED decreases so that a heating valuedecreases. Therefore, it is possible to enhance thermal stability of thevertical LED, thereby enhancing characteristics and reliability of thevertical LED.

Although a few embodiments of the present general inventive concept havebeen shown and described, it will be appreciated by those skilled in theart that changes may be made in these embodiments without departing fromthe principles and spirit of the general inventive concept, the scope ofwhich is defined in the appended claims and their equivalents.

What is claimed is:
 1. A vertical light emitting diode (LED) comprising:an n-electrode; an n-type GaN layer formed under the n-electrode, a Ga⁺Nlayer formed over an entire surface of the n-type GaN layer and underthe electrode, the Ga⁺N layer having a surface with an N-polar surfacepolarity, which contacts the n-electrode, and containing more Ga than N;an active layer formed under the n-type GaN layer; a p-type GaN layerformed under the active layer; a p-electrode formed under the p-type GaNlayer; and a structure support layer formed under the p-electrode,wherein the Ga⁺N layer coming in contact with the n-electrode hassurface irregularities formed thereon, wherein the n-electrode contactswith the part of the Ga⁺N layer.
 2. The vertical LED according to claim1, wherein the n-electrode is formed of a single layer composed of oneor more metals selected from the group consisting of Ti, Ta, and Zr. 3.The vertical LED according to claim 1, wherein the n-electrode is formedof a multilayer in which more than two layers including a layer composedof one or more metals selected from the group consisting of Ti, Ta, andZr are laminated.
 4. The vertical LED according to claim 1, wherein theGa⁺N layer of the n-type GaN layer is formed by laser-treating thesurface of the n-type GaN layer coming in contact with the n-electrode.5. The vertical LED according to claim 1, wherein the Ga⁺N layer of then-type GaN layer is formed by heat-treating the surface of the n-typeGaN layer coming in contact with the n-electrode.
 6. The vertical LEDaccording to claim 1, wherein the p-electrode is formed of a conductivereflecting member.
 7. The vertical LED according to claim 1, wherein then-type GaN layer includes a Ga layer, the Ga⁺N layer and a GaN layersequentially laminated from the surface of the n-type GaN layer facingthe n-electrode.